identical to the second byte in the immediately preceding pair, then the expected redundant code is ignored. If there are printing characters in place of the redundant code, they will be processed normally.

(5) There is provision for decoding a second data channel. The second data channel is encoded with the same control codes and procedures already described. The first byte of every control code pair indicates the data channel (C1/C2) to which the command applies. Control codes which do not match the data channel selected by the user, and all subsequent data related to that control code, are ignored by the receiver.

MID-ROW CODES

Rows. Roll-Up Captions-3

Rows.

ory.

Carriage Return. Erase Non-Displayed

Memory.

11 2D

19 2D Magenta Underline.

(1) Data rejection. The receiver should provide an effective procedure to verify data. A receiver will reject data if the data is invalid, or if the data is directed to the data channel or field not selected by the user. Invalid data is any data that fails to pass a check for odd parity, or which, having passed the parity check, is assigned no function.

(1) If a print character fails to pass a check for parity, a solid block (7Fh) should be displayed in place of the failed character. In addition, valid data can be corrupted in many ways and may not be suitable for display. For example, repeated fields, skipped fields and altered field sequences are all possible from consumer video equipment and might present meaningless captions.

(2) The receiver will ignore data rejected due to being directed to a deselected field or channel. However, this will not cause the display to be disabled.

(k) Automatic display enable/disable. The receiver shall provide an automatic enable/disable capability to prevent the display of invalid or incomplete data, when the user selects the Caption Mode. The display should automatically become enable after the receiver verifies the data as described in paragraph (j) of this section. The display will be automatically disabled when there is a sustained detection of invalid data. The display will be re-enabled when the data verification process has been satisfied once again.

(1) Compatibility with Cable Security Systems. Certain cable television security techniques, such as signal encryption and copy protection, can alter the television signal so that some methods of finding line 21 will not work. In particular, counting of lines or timing from the start of the vertical blanking interval may cause problems. Caption decoding circuitry must function properly when receiving signals from cable security systems that were designed and marketed prior to April 5, 1991. Further information concerning such systems is available from the National Cable Television Association, Inc., Washington, DC, and from the Electronic Industries Association, Washington, DC.

(m) Labelling and consumer information requirements. The box or other package in which the individual television receiver is to be marketed shall carry a statement in a prominent location, visible to the buyer before purchase, which reads as follows:

This television receiver provides display of television closed captioning in accordance with §15.119 of the FCC rules.

Receivers that do not support color attributes or text mode, as well as receivers that display only upper-case characters pursuant to paragraph (g) of this section, must include with the statement, and in the owner's manual, language indicating that those features are not supported.

(n) Glossary of terms. The following terms are used to describe caption decoder specifications:

(1) Base row: The bottom row of a roll-up display. The cursor always remains on the base row. Rows of text roll upwards into the contiguous rows immediately above the base row.

(2) Box: The area surrounding the active character display. In Text Mode, the box is the entire screen area defined for display, whether or not displayable characters appear. In Caption Mode, the box is dynamically redefined by each caption and each element of displayable characters within a caption. The box (or boxes, in the case of a multiple-element caption) inIcludes all the cells of the displayed characters, the non-transparent spaces between them, and one cell at the beginning and end of each row within a caption element in those decoders that use a solid space to improve legibility.

(3) Caption window: The invisible rectangle which defines the top and bottom limits of a roll-up caption. The window can be 2 to 4 rows high. The lowest row of the window is called the base row.

(4) Cell: The discrete screen area in which each displayable character or space may appear. A cell is one row high and one column wide.

(5) Column: One of 32 vertical divisions of the screen, each of equal width, extending approximately across the full width of the safe caption area as defined in paragraph (n)(12) of this section. Two additional columns, one at the left of the screen and one at the

341-180 0-93-19

right, may be defined for the appearance of a box in those decoders which use a solid space to improve legibility, but no displayable characters may appear in those additional columns. For reference, columns may be numbered 0 to 33, with columns 1 to 32 reserved for displayable characters.

(6) Displayable character-Any letter, number or symbol which is defined for on-screen display, plus the 20h space.

(7) Display disable: To turn off the display of captions or text (and accompanying background) at the receiver, rather than through codes transmitted on line 21 which unconditionally erase the display. The receiver may disable the display because the user selects an alternate mode, e.g., TV Mode, or because no valid line 21 data is present.

(8) Display enable: To allow the display of captions or text when they are transmitted on line 21 and received as valid data. For display to be enabled, the user must have selected Caption Mode or Text Mode, and valid data for the selected mode must be present on line 21.

(9) Element: In a pop-on or paint-on style caption, each contiguous area of cells containing displayable characters and non-transparent spaces between

those characters. A single caption may have multiple elements. An element is not necessarily a perfect rectangle, but may include rows of differing widths.

(10) Erase Display: In Caption Mode, to clear the screen of all characters (and accompanying background) in response to codes transmitted on line 21. (The caption service provider can accomplish the erasure either by sending an Erase Displayed Memory command or by sending an Erase Non-Displayed Memory command followed by an End of Caption command, effectively making a blank caption "appear".) Display can also be erased by the receiver when the caption memory erasure conditions are met, such as the user changing TV channels.

(11) Row: One of 15 horizontal divisions of the screen, extending across the full height of the safe caption area as defined in paragraph (n)(12) of this section.

(12) Safe caption area: The area of the television picture within which captioning and text shall be displayed to ensure visibility of the information on the majority of home television receivers. The safe caption area is specified as shown in the following figure:

unique one-byte codes which are the same in either data channel.

(14) Text: When written with an upper-case "T", refers to the Text Mode. When written with a lower-case "t", refers to any combination of displayable characters.

(15) Transparent space: Transmitted as a special character, it is a one-column-wide space behind which program video is always visible (except when a transparent space immediately precedes or follows a displayable character and solid box is needed to make that character legible).

[56 FR 27201, June 13, 1991, as amended at 57 FR 19094, May 4, 1992; 58 FR 44893, Aug. 25, 1993]